it used its horns during battle
it had bird-like hind limbs
it ate leaves from very tall plants
Correct!
Birds are a kind of theropod and have the same type of hind limbs as a Chirostenotes, another theropod.
Chirostenotes pergracilis
Only a few fossils of this Chirostenotes have been found. It has some bird-like features. Its lower jaws look like a bird's beak. It was mistaken for a giant bird for a while. Recently, a good specimen was found. Now we know that this animal was a close relative of Oviraptor.